Numerous medication infusion devices which sit directly on top of a patient's skin have been developed. Such devices typically operate as follows. A housing of the device is placed on the patient's skin such that an infusion cannula (extending downwardly therefrom) pierces through the patient's skin. Typically, the housing is placed against the patient's skin by use of an inserter needle assembly. Specifically, an insertion needle on the inserter needle assembly is received through the housing, passing through the center of the infusion cannula. The main body of the inserter needle assembly is then used to press down against the housing, pushing the housing down against the patient's skin while the inserter needle guides the infusion cannula into the patient. Then, the inserter needle assembly is removed, pulling the inserter needle out of the housing, and leaving the hollow infusion cannula in the patient for delivery of medication therethrough. Then, a connecting hub is typically attached onto the housing. Fluid medication is then infused into the connecting hub, passing sequentially through the housing and the infusion cannula and into the patient. Examples of such systems are found in U.S. Pat. No. 6,056,718 and U.S. Pat. No. 6,685,674.
As can be seen, a problem common to these systems is that both the inserter needle and an infusion needle (in the connecting hub) pass through the septum in the same location. This is due to the fact that in existing designs, the infusion cannula, inserter needle, and infusion needle are all co-linear with one another.
A disadvantage of this common design is that the septum must be pierced in the same location by both the inserter needle (which is removed after the housing is placed onto the patient's skin) and the infusion needle (which passes through the septum when the connecting hub is attached to the housing). Re-using the same location in the septum for two different needle entries has the potential for causing septum wear and leakage. As will be further explained herein, other disadvantages of such “in-line” designs also exist.